Method for drivingly controlling a variable reluctance type motor

ABSTRACT

A drive control method for a variable reluctance type motor capable of improving the motor efficiency by preventing generation of a disturbance torque. In function generators (8A to 8C) of a controller for embodying the method, the motor rotation direction and the motor driving mode are determined based on the generation order of A- and B-phase feedback pulses from a pulse coder (7) and the sign of a torque command (Tc) from a speed loop compensation circuit (1), and, on the basis of the determination results, either one of four excitation patterns is selected. Function signal values corresponding to actual motor electrical angles (θ) are generated from the function generators in accordance with the selected excitation pattern, and excitation of individual phases of the motor (6) is controlled by power amplifiers (4A to 4C) which respond to voltage commands derived based on these function signal values. The excitation interruption timing is so determined as to extinguish a winding current before a disturbance torque is generated by the current which is caused to flow, due to the presence of the inductance of the stator winding, in this winding after the excitation interruption.

BACKGROUND OF THE INVENTION

The present invention relates to a method for drivingly controlling avariable reluctance type motor, and more particularly, to a drivecontrol method of this kind capable of improving the efficiency of amotor.

A variable reluctance type motor, which comprises a stator having aplurality of salient poles around which windings are wound and a rotorhaving a plurality of salient poles, is so arranged as to rotate therotor by attracting a rotor salient pole near an excited stator salientpole towards the stator salient pole by a magnetic attraction forcecaused by the excited stator salient pole. At this time, the rotarytorque applied to the rotor acts in a direction to reduce the magneticresistance between the stator salient pole and the rotor salient pole,irrespective of the direction of a current flowing in the statorwinding. That is, during the rotor rotation, the rotary torque acting inthe direction of the rotor rotation is applied to the rotor from aninstant at which the rotor salient pole starts to face the excitedstator salient pole (unalign position) until an instant at which therotor salient pole is brought to completely face the stator salient pole(align position). Thereafter, when the rotor further continues to rotatein the same direction, the rotary torque acting in a direction oppositeto the rotation direction of the rotor is applied to the rotor salientpole until the rotor salient pole starts to be deviated from a statewhere it faces the stator salient pole.

For example, in case that the rotor 21 rotates in a counterclockwisedirection relative to the stator 20 as shown in FIGS. 4A and 4B, therotary torque acting in the rotor rotation direction or thecounterclockwise direction is applied to a rotor salient pole 21a fromthe time when the leading edge 21a', as viewed in the rotor rotationdirection, of the rotor salient pole 21a has reached a position on anextension of the leading edge 20A' of an excited stator salient pole 20Aof A-phase and hence the rotor salient pole 21a has reached that rotaryposition unalign position (electrical angle of 0 degree) of the rotorwhich is shown in FIG. 4A at which it starts to face the stator salientpole 20A until the time at which the rotor salient pole 21a has reacheda rotor rotary position align position (electrical angle of 180 degrees)shown in FIG. 4B at which it completely faces the stator salient pole20A, with the axes of the rotor salient pole 21a and the stator salientpole 20A brought to be coincide with each other. When the rotor 21continues to further rotate in the counterclockwise direction afterhaving reached the rotor rotation position shown in FIG. 4B, the rotarytorque acting in a direction opposite to the rotor rotation direction orthe clockwise direction is applied to the rotor salient pole 21a untilthe trailing edge 21a" of the rotor salient pole 21a reaches a positionon the extension unalign position (again) (electrical angle of 360degrees) of the trailing edge 20A" of the stator salient pole 20A andhence the rotor salient pole 21a starts to be deviated from a statewhere it faces the stator salient pole 20A. At the time of releasingfrom the state where the rotor salient pole 21a faces the stator salientpole 20A, the leading edge 21d' of the next rotor salient pole 21dreaches a position on the extension of the leading edge 20A' of thestator salient pole 20A, so that the rotor salient pole 21d starts toface the stator salient pole 20A.

After all, the acting direction of the rotary torque caused when astator salient pole of a certain phase is excited is determined independence on the rotary position (electrical angle) of the rotorrepresenting the positional relation between the stator salient pole andthe rotor salient pole. Thus, in order to cause the variable reluctancetype motor to rotate in a desired direction, the respective statorsalient poles are sequentially excited in a desired order for a desiredperiod of time in accordance with the rotary position of the rotor. Forexample, in an example shown in FIGS. 4A and 4B, if the rotor 21 is tobe rotated counterclockwise, an A-phase stator winding (not shown) woundaround the stator salient pole 20A is energized in a rotor rotationregion represented by an electrical angle region of 0 to 180 degrees. Onthe other hand, in the case of rotating the rotor 21 clockwise, theA-phase stator winding is energized in a rotor rotation region indicatedby an electrical angle region of 180 to 360 degrees. Conventionally, inorder to control the drive of the variable reluctance type motor, datais read out from a read only memory, in which the above two types ofexcitation patterns are previously stored, in accordance with the rotaryposition of the rotor, so that the stator windings of respective phasesare each energized in a desired order for a desired period of time.

However, due to the presence of an inductance of the stator winding, acurrent continues to flow in the winding for a certain period of timeafter excitation of the stator winding is interrupted. For example, in acase where the A-phase stator winding is energized for an excitationsection T1 corresponding to an electrical angle region of 0 to 180degrees of the rotor in order to rotate the rotor 21 in thecounterclockwise direction, a current will flow in the stator windingeven in a section T2 corresponding to rotor electrical angle positionswhich exceed 180 degrees, as shown in FIG. 5. As a result, a disturbancetorque acting to rotate the rotor in a direction opposite to the desiredrotation direction is generated. Hence, energy is consumed to cancel thedisturbance torque, so that the motor efficiency will be lowered.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for drivinglycontrolling a variable reluctance type motor, which is capable ofreducing or preventing generation of a disturbance torque acting torotate a rotor in a direction opposite to a desired rotation direction,thereby improving motor efficiency.

In order to attain the above object, according to the present invention,there is provided a drive control method for use in a variablereluctance type motor which includes a stator having a plurality ofsalient poles around which windings are wound and a rotor having aplurality of salient poles, the motor being driven in that motor drivingmode which is determined in dependence on a difference between a commandvalue of a motor driving parameter and an actual value thereof and whichis one of an acceleration mode where a torque acting in a rotationdirection of the motor is generated and a deceleration mode where atorque acting in a direction opposite to the rotor rotation direction isgenerated. The drive control method comprises the steps of: (a) startingexcitation of the winding of a to-be-excited stator salient pole when arotor salient pole near the to-be-excited stator salient pole hasreached a first predetermined rotary position which is determined independence on the motor driving mode, so as to generate a desired torqueacting in a rotation direction suited to the motor driving mode; and (b)interrupting the excitation started in the step (a) when the rotorsalient pole has reached a third predetermined rotary position short ofa second predetermined rotary position which cooperates with the firstpredetermined rotary position to define a predetermined rotary angleregion where the desired torque is generated by an electric currentflowing in the winding associated with the step (a), so as to prevent anelectric current from flowing in the winding in a region other than thepredetermined rotary angle region.

Preferably, in the acceleration mode, a determination to the effect thatthe rotor salient pole has reached the first predetermined rotaryposition is made when the rotor salient pole starts to face the statorsalient pole. In the deceleration mode, a determination to the effectthat the rotor salient pole has reached the first predetermined positionis made when the rotor salient pole is brought to completely face thestator salient pole. Further, the second predetermined rotary positionin the acceleration mode is set such that the rotor salient pole willcompletely face the stator salient pole at that rotary position, and thesecond predetermined rotary position in the deceleration mode is setsuch that the rotor salient pole will start to be deviated at thatrotary position from a state where it faces the stator salient pole. Thethird predetermined rotary position is set in dependence on theinductance of the winding. Further, a motor rotation speed is used asthe motor driving parameter, and either one of the acceleration mode andthe deceleration mode is selected in accordance with the differencebetween a command value of the motor rotation speed and an actual valuethereof. More preferably, the excitation of the winding of the nextstator salient pole is started before the third predetermined rotaryposition is reached.

As described above, according to the present invention, excitation ofthe winding of the stator salient pole is started when the rotor salientpole has reached the first predetermined rotary position determined independence on the motor driving mode, and the excitation is interruptedwhen the rotor has reached the third predetermined rotary position shortof the second predetermined rotary position which cooperates with thefirst predetermined rotary position to define the predetermined rotaryangle region where a desired torque acting in the rotation directionsuited to the motor driving mode is generated by an electric currentflowing in the winding. Therefore, an electric current caused by theinductance of the winding to flow in the winding after the interruptionof the excitation is significantly reduced or extinguished before adisturbance torque acting in a direction opposite to the intended actingdirection is generated by the above electric current. As a result, noenergy is consumed to cancel the disturbance torque, whereby the motorefficiency can be improved.

Preferably, excitation of the winding of the next stator salient pole isstarted before the third predetermined rotary position is reached, sothat the rotary torque can be continuously generated to smoothly rotatethe motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a graph showing an excitation section and an actual windingcurrent in the present invention in a case where a variable reluctancetype motor is deceleratingly operated in a counterclockwise direction;

FIG. 1B is a graph, similar to FIG. 1A, for a case where the motor isacceleratingly operated in the counterclockwise direction;

FIG. 1C is a graph, similar to FIG. 1A, for a case where the motor isacceleratingly operated in a clockwise direction;

FIG. 1D is a graph, similar to FIG. 1A, for a case where the motor isdeceleratingly operated in the clockwise direction;

FIG. 2A is a graph showing an excitation section in a case where a3-phase variable reluctance type motor is deceleratingly operated in thecounterclockwise direction by means of a drive control method accordingto one embodiment of the present invention;

FIG. 2B is a graph, similar to FIG. 2A, for a case where the motor isacceleratingly operated in the counterclockwise direction;

FIG. 2C is a graph, similar to FIG. 2A, for a case where the motor isacceleratingly operated in the clockwise direction;

FIG. 2D is a graph, similar to FIG. 2A, for a case where the motor isdeceleratingly operated in the clockwise direction;

FIG. 3 is a block diagram showing essential part of a controller forembodying the method according to the embodiment shown in FIGS. 2A to2D;

FIG. 4A is a fragmentary schematic view showing a variable reluctancetype motor in a state where a rotor salient pole (unalign position)starts to face a stator salient pole;

FIG. 4B is a view, similar to FIG. 4A, showing a state where the rotorsalient pole completely faces the stator salient pole (align position);

FIG. 5 is a graph showing an excitation section and an actual windingcurrent in a conventional method of drivingly controlling a variablereluctance type motor, and;

FIG. 6 is a vertical sectional view of a 3-phase variable reluctancetype motor, without windings, for use in the drive control method shownin FIGS. 2A-2D.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIGS. 1 and 4, the principle of a method, according tothe present invention, for drivingly controlling a reluctance type motorwill be explained.

In the present invention, one of four excitation patterns is selectedaccording to whether the motor is to be rotated in a clockwise directionor counterclockwise direction and whether a motor driving mode, which isdetermined in dependence on the difference between a command value of amotor driving parameter (e.g., motor rotation speed) and an actual valuethereof, is either an acceleration mode for generating a torque actingin the motor rotation direction or a deceleration mode for generating atorque acting in a direction opposite to the motor rotation direction.

In the case of driving the motor in the deceleration mode while it isbeing rotated in the counterclockwise direction, an excitation patternshown in FIG. 1A is selected. According to this excitation pattern, whenthe rotor 21 has reached a rotary position (FIG. 4B) indicated by anelectrical angle of 180 degrees (align position) and hence the rotorsalient pole 21a is brought to completely face the stator salient pole20A, a determination to the effect that the starting point of theexcitation section T is reached is made, so that excitation of thewinding (not shown) of the stator salient pole 20A is started. As aresult, a torque acting in the clockwise direction which is opposite tothe motor rotation direction is generated, so that the motor isdeceleratingly operated. Thereafter, the excitation of the winding isinterrupted before an electrical angle at 360 degrees (unalignposition); and the rotor salient pole 21a starts to be deviated from astate where it faces the stator salient pole 20A. In practice, after theinterruption of excitation, and electric current I flows in the windingbecause of the presence of the inductance of the winding. Therefore, theexcitation section T, particularly the termination end thereof, isproperly set, so that the winding current I assumes a value of zero orclose to zero when the rotor salient pole 21a has reached that rotaryposition which is represented by an electrical angle of 360 degrees andwhich corresponds to the rotary position of the rotor salient pole 21bshown in FIG. 4A, and hence the rotor salient pole 21a starts to bedeviated from the state where it faces the stator salient pole 20A. As aresult, the stator salient pole 20A is de-energized when the facingstate between the rotor salient pole 21a and the stator salient pole 20Astarts to be broken, that is, when the next rotor salient pole 21d hasreached a rotary position corresponding to the rotary position of therotor salient pole 21a shown in FIG. 4A. Therefore, the rotor salientpole 21d will not be magnetically attracted by the stator salient pole20A, and no torque acting in the counterclockwise direction isgenerated, so that the deceleration operation of the motor will not bedisturbed.

In a case where the motor is driven in the acceleration mode while it isbeing rotated in the counterclockwise direction, an excitation patternshown in FIG. 1B is selected. When the rotor 21 has reached a rotaryposition of FIG. 4A indicated by an electrical angle of 0 degree, andthe rotor salient pole 21a starts to face the stator salient pole 20A,excitation of the winding of the stator salient pole 20A is started. Asa result, a torque acting in the counterclockwise direction, which isthe same as the motor rotation direction, is generated, whereby themotor is operated acceleratingly. Thereafter, the excitation of thewinding is interrupted before the rotor salient pole 21a is brought tocompletely face the stator salient pole 20A (align position). As aresult, the winding current I assumes a value of zero or close to zerowhen the rotor salient pole 21a has reached a rotary position indicatedby an electrical angle of 180 degrees (unalign position) andcorresponding to the rotary position shown in FIG. 4B, and hence therotor salient pole 21a is brought to completely face the stator salientpole 20A. As a result, the stator salient pole 20A is de-energized whenthe rotor salient pole 21a starts to be further rotated in thecounterclockwise direction. Therefore, the rotor salient pole 21a willnot be magnetically attracted by the stator salient pole 20A, and notorque acting in the clockwise direction and disturbing the acceleratingoperation is generated.

According to an excitation pattern of FIG. 1C which is selected in acase where the motor is to be driven in the acceleration mode while themotor is being rotated in the clockwise direction, which is opposite tothe motor rotation direction in the case of FIGS. 4A and 4B, excitationof the winding of the stator salient pole 20A is started when the rotor21 has reached a rotary position of FIG. 4A indicated by an electricalangle of 360 degrees (unalign position) and hence the rotor salient pole21b starts to face the stator salient pole 20A, so that a torque actingin the clockwise direction which is the same as the motor rotationdirection is generated, whereby the motor is acceleratingly operated.Thereafter, the excitation of the winding is interrupted before therotor salient pole 21b is brought to completely face the stator salientpole 20A. Then, the winding current I assumes a value of zero or closedto zero when the rotor salient pole 21b has reached a rotary positionindicated by an electrical angle of 180 degrees (align position) andcorresponding to the rotary position of the rotor 21a shown in FIG. 4B,with the rotor salient pole 21a brought to completely face the statorsalient pole 20A. As a result, the stator salient pole 20A isde-energized when the rotor salient pole 21b starts to be furtherrotated in the clockwise direction. Therefore, the rotor salient pole21b will not be magnetically attracted by the stator salient pole 20A,and hence no torque acting in the counterclockwise direction anddisturbing the accelerating operation is generated.

In a case where the motor is to be driven in the deceleration mode whileit is being rotated in the clockwise direction, excitation of thewinding of the stator salient pole 20A is started, in accordance with anexcitation pattern shown in FIG. 1D, when the rotor 21 has reached arotary position of FIG. 4B indicated by an electrical angle of 180degrees (align position) so that the rotor salient pole 21a is broughtto completely face the stator salient pole 20A. Accordingly, a torqueacting in the counterclockwise direction which is opposite to the motorrotation direction is generated, whereby the motor is operateddeceleratingly. Thereafter, the excitation of the winding is interruptedbefore the rotor salient pole 21a starts to be deviated from the statein which it faces the stator salient pole 20A, whereby the current I iscaused to assume a value of zero or close to zero when the rotor salientpole 21a has reached a rotary position indicated by an electrical angleof 0 degree (unalign position) and shown in FIG. 4A, and when the rotorsalient pole 21a starts to be deviated from the facing state betweenitself and the stator salient pole 20A. As a result, the stator salientpole 20A is de-energized when the facing state between the rotor salientpole 21a and the stator salient pole 20A starts to be broken, that is,when the next rotor salient pole 21b has reached the rotary positionshown in FIG. 4A and starts to face the stator salient pole 20A.Therefore, the rotor salient pole 21b will not be magnetically attractedby the stator salient pole 20A, and no torque acting in the clockwisedirection and disturbing the deceleration operation is generated.

The above four excitation patterns, particularly the electrical anglepositions of the rotor at the time of excitation interruption in therespective excitation patterns, are determined, for instance, by actualmeasurements conducted while the motor is being rotated at a rotationalspeed at the time of use of the motor. Preferably, in a multi-phasemotor, the electrical angles of the rotor at the excitation startingtime and excitation interruption time are determined in such a mannerthat the difference between the electrical angles of the rotor at theexcitation starting time and excitation interruption time never besmaller than an electrical angle derived by dividing the electricalangle of 360 degrees by the number of motor phases. By this electricalangle determination, a stator winding of either one of the phases of themulti-phase motor is necessarily excited in any motor rotary position,so that a motor rotation angle region where no motor output torque isgenerated never appears.

In the following, with reference to FIGS. 2A to 2D, a drive controlmethod according to one embodiment of the present invention for use in a3-phase variable reluctance type motor (shown in FIG. 6) will beexplained.

The present embodiment is so arranged as to control the excitation ofthe stator winding of each phase in accordance with that correspondingone of the four excitation patterns which is determined in dependence onthe motor rotation direction and the motor driving mode. Further, theexcitation section T of each phase of the motor is set to have anelectrical angle of 135 degrees. That is, the excitation is interruptedwhen the rotor has rotated through an electrical angle of 135 degreesafter start of the excitation. The electrical angle shown in the drawingis associated with the A-phase excitation pattern, and the B- andC-phases are shifted with respect to the A-phase by 120 and 240 degrees,respectively.

In a case where the motor is to be driven in the deceleration mode whilethe motor is being rotated in the counterclockwise direction, theexcitation of the A-, B- and C-phase stator windings is controlled inaccordance with the excitation pattern of FIG. 2A. When that rotaryposition of the rotor is reached, which is indicated by an electricalangle of 180 degrees and at which the rotor salient pole completelyfaces the A-phase stator salient pole, the excitation of the A-phasestator winding is started to excite the A-phase stator salient pole,whereby a torque acting in the clockwise direction which is opposite tothe motor rotation direction is generated, and the motor is operateddeceleratingly. Thereafter, when the rotor is further rotated by anelectrical angle of 15 degrees and reaches the rotary position indicatedby an electrical angle of 195 degrees (=180 degrees+15 degrees), theC-phase excitation started as will be described later is interrupted.

When the rotor is further rotated by an electrical angle of 120 degreesfrom the A-phase excitation starting time and reaches the rotaryposition indicated by an electrical angle of 300 degrees (=180degrees+120 degrees), another rotor salient pole (hereinafter referredto as a second rotor salient pole) is brought to completely face theB-phase stator salient pole. At this time, the B-phase excitation isstarted to excite the stator salient pole so that a torque acting in theclockwise direction to decelerate the motor is generated. When the rotoris further rotated by an electrical angle corresponding to the A-phaseexcitation section T from the A-phase excitation starting time andreaches the rotary position indicated by an electrical angle of 315degrees (=180 degrees+135 degrees), the A-phase excitation isinterrupted. Even after the interruption of excitation, an electriccurrent is caused to continuously flow in the A-phase stator winding dueto the presence of the inductance of the winding, whereby a torque whichacts to decelerate the motor is generated. On the other hand, however,when the rotor has reached the rotary position indicated by anelectrical angle of 360 degrees or a position in the vicinity of thatrotary position, the winding current is extinguished, thereby preventinggeneration of a torque which accelerates the motor.

When the rotor is rotated by an electrical angle of 120 degrees from theB-phase excitation starting time and reaches the rotary positionindicated by an electrical angle of 60 degrees (=300 degrees+120degrees) and hence the second rotor salient pole is brought tocompletely face the C-phase stator salient pole, excitation of theC-phase stator winding is started. When the rotor is further rotated byan electrical angle of 15 degrees from the C-phase excitation startingtime and reaches the rotary position indicated by an electrical angle of75 degrees (=420 degrees+15 degrees=300 degrees+135 degrees) andcorresponding to the termination end of the B-phase excitation sectionT, the B-phase excitation is interrupted. The B-phase winding current iscaused to continuously flow due to the presence of the inductance of thewinding until the rotary position indicated by an electrical angle of120 degrees is reached, so that the torque which acts to decelerate themotor is generated.

When the rotor is rotated through an electrical angle of 15 degrees toreach the rotary position (an electrical angle of 195 degrees)corresponding to the termination end of the C-phase excitation section Tafter the rotor rotary position of an electrical angle of 180 degreeshas been reached and the A-phase excitation has been started again, theC-phase excitation is interrupted as described before. Due to thepresence of the inductance of the winding, an electric current is causedto continuously flow in the C-phase stator winding until the rotorrotary position of an electrical angle of 240 degrees is reached, so asto generate a torque which decelerates the motor. Subsequently, the A-,B- and C-phase excitation control operations are repeated, whereby themotor is operated deceleratingly.

In case that the motor is acceleratingly operated while it is beingrotated in the counterclockwise direction according to the excitationpattern of FIG. 2B, the A-phase excitation is started at that rotorrotary position (an electrical angle of 0 degree) at which the rotorsalient pole starts to face the A-phase stator salient pole, whereas theA-phase excitation is interrupted at that rotary position (an electricalangle of 135 degrees) which is short, by an electrical angle of 45degrees, of that rotor rotary position (an electrical angle of 180degrees) at which the rotor salient pole completely faces the A-phasestator salient pole. Further, the B-phase excitation which has beenstarted at the rotary position (an electrical angle of 120 degrees) atwhich the rotor salient pole starts to face the B-phase stator salientpole is interrupted at the rotary position (an electrical angle of 255degrees) which is short, by an electrical angle of 45 degrees, of therotary position at which the rotor salient pole completely faces theB-phase stator salient pole. Furthermore, the C-phase excitation iseffected in a rotor rotary angle region corresponding to an electricalangle region of 240 to 15 degrees. The torque acting in thecounterclockwise direction is applied to the rotor with the excitationof the individual phases, whereas the winding current caused to flowafter the interruption of excitation is rendered to be extinguishedbefore it acts to generate a substantial torque exerting in theclockwise direction.

In case that the motor is acceleratingly operated while it is beingrotated in the clockwise direction, the A-, B- and C-phase excitationoperations are started at those rotary positions (electrical angles of360 degrees, 120 degrees and 240 degrees) at which the rotor salientpole starts to face the A-, B- or C-phase stator salient poles as shownin FIG. 2C, so that a torque acting in the clockwise direction toaccelerate the motor is generated by the excitation. Thereafter, theexcitation is interrupted when the rotor is rotated by a rotation angle,corresponding to the excitation section T of an electrical angle of 135degrees, to reach the rotary position (an electrical angle of 225degrees, 345 degrees or 105 degrees) corresponding to the terminationend of the excitation section T. A winding current caused to flow afterthe interruption of excitation is extinguished before it generates asubstantial torque acting in the counterclockwise direction.

In case that the motor is deceleratingly operated while it is beingrotated in the clockwise direction, the A-, B- and C-phase excitationoperations are started at the respective rotor rotary positions(electrical angles of 180 degrees, 300 degrees and 60 degrees) at whichthe rotor salient pole completely faces the A-, B- or C-phase statorsalient poles as shown in FIG. 2D, and a torque acting in thecounterclockwise direction is generated by the excitation so that themotor is decelerated. Thereafter, the excitation is interrupted when therotor is rotated by a rotation angle of an electrical angle of 135degrees to reach the rotary position (an electrical angle of 45 degrees,165 degrees or 285 degrees) corresponding to the termination end of theexcitation section T. A winding current caused to flow after theinterruption of excitation is extinguished before it generates asubstantial torque in the clockwise direction.

In the following, a controller for embodying the method of the aboveembodiment will be explained with reference to FIG. 3.

The controller comprises A-, B- and C-phase function generators 8A, 8Band 8C each of which includes a read only memory (ROM), not shown,storing therein four types of excitation patterns (FIGS. 2A to 2D). Eachof the excitation patterns consists of function signal valuesrespectively set for each rotor electrical angle region, and thoseexcitation patterns stored in the ROMs which correspond to one anotherare different in phase from one another by an electrical angle of 120degrees.

The controller further comprises a frequency-to-voltage converter 9 forconverting the frequency at which A- or B-phase feedback pulses aresequentially delivered from a pulse coder 7 mounted on a 3-phasevariable reluctance type motor 6 with rotation of the motor into avoltage representative of the actual motor speed, and a speed loopcompensation circuit 1 for amplifying the difference (speed deviation)between a speed command Vc supplied from a host controller, not shown,and an output of the converter 9, to thereby generate a torque commandTc. Each of the function generators 8A to 8C, which is connected to thepulse coder 7 and the compensation circuit 1, is arranged to determinethe rotation direction of the motor in accordance with the generationorder of the A- and B-phase feedback pulses, and determine the motordriving mode in accordance with the positive or negative sign of thetorque command Tc. Further, each function generator is arranged togenerate that one of the function signal values, constituting thepredetermined excitation patterns selected in accordance with theresults of both the determinations, which corresponds to an actual rotorelectrical angle θ represented by the feedback pulses from the pulsecoder 7.

Moreover, the controller comprises multipliers 2A to 2C for multiplyingthe function signal value from a corresponding one of the functiongenerators 8A to 8C by the torque command Tc from the compensationcircuit 1 to generate current commands ir(A) to ir(C), current detectors5A to 5C, current loop compensation circuits 3A to 3C for respectivelyamplifying differences (current deviations) between corresponding onesof actual currents ic(A) to ic(C) detected by the current detectors andthe current commands ir(A) to ir(C) to generate voltage commands er(A)to er(C), and power amplifiers 4A to 4C, each comprised of a PWMinverter and the like, for respectively converting the voltage commandser(A) to er(C) into voltages er'(A) to er'(C) applied to the individualphases of the motor 6.

In FIG. 3, symbols G1(S) and G2(S) respectively denote the transferfunction of the speed loop compensation circuit 1 and the transferfunction of each of the current loop compensation circuits 3A to 3C, anda symbol G3 denotes the gain of each of the power amplifiers 4A to 4C.

In the following, the operation of the controller of FIG. 3 will beexplained.

The generation frequency of the A- or B-phase feedback pulsessequentially generated from the pulse coder 7 with rotation of the motor6 is converted, in the frequency/voltage converter 9, into a voltagerepresentative of an actual motor speed. Then, in the speed loopcompensation circuit 1, a torque command Tc is created in accordancewith the deviation between the speed command Vc from the host controllerand an output of the converter 9. Each of the function generators 8A to8C determines the motor rotation direction and the motor driving mode onthe basis of the generation order of the A- and B-phase feedback pulsesand the sign of the torque command Tc, and selects one of the four typesof excitation patterns shown in FIGS. 2A to 2D in accordance with theresults of these determinations. For example, if it is determined thatthe motor 6 should be driven in the counterclockwise direction in thedeceleration mode, each of the function generators 8A to 8C selects theexcitation pattern of FIG. 2A and then supplies that one of the functionsignal values constructing the thus selected excitation pattern whichcorresponds to an actual motor electrical angle θ represented by thefeedback pulses from the pulse coder 7. The current commands ir(A) toir(C) are derived in the multipliers 2A to 2C on the basis of thefunction signal values from the function generators 8A to 8C and thetorque command Tc, and actual currents ic(A) to ic(C) are detected bymeans of the current detectors 5A to 5C. Then, the voltage commandser(A) to er(C) derived in the loop compensation circuits 3A to 3C on thebasis of the current commands and the actual currents are converted intovoltage commands er(A) to er(C) in the power amplifiers 4A to 4C andthen applied to the individual phases of the motor.

Subsequently, a proper excitation pattern is selected in accordance withthe speed command Vc and the feedback pulses, and function signal valuesconstructing the selected excitation pattern are sequentially read outwith rotation of the motor and supplied for the motor control. As aresult, the motor 6 is driven in the acceleration mode or decelerationmode, so that the motor 6 is rotated in a desired direction at a desiredspeed. In addition, as described with reference to FIGS. 2A to 2D, anelectric current caused to flow in each of the stator windings of theindividual phases of the motor 6 due to the presence of inductance ofeach winding after the interruption of excitation of that winding aextinguished or markedly reduced before the same current acts togenerate a disturbance torque exerting in a direction opposite to adesired motor rotation direction. Therefore, generation of a substantialdisturbance torque can be prevented, whereby the motor efficiency can beimproved.

We claim:
 1. A drive control method for a variable reluctance type motorcomprising a stator having a plurality of salient poles around whichwindings are wound and a rotor having a plurality of salient poles, themotor being driven in a motor driving mode which is determined independence on a difference between a command value of a motor drivingparameter and an actual value, the motor driving mode being one of anacceleration mode where a torque acting in a rotation direction of therotor is generated and a deceleration mode where a torque acting in adirection opposite to the rotor rotation direction is generated, saidmethod comprising the steps of:(a) starting excitation of the winding ofa to-be-excited stator salient pole when a rotor salient pole near theto-be-excited stator salient pole has reached a first predeterminedrotary position determined in dependence on the motor driving mode, forgenerating a desired torque acting in a rotation direction suited to themotor driving mode; and (b) interrupting the excitation started in saidstep (a) when the rotor salient pole has reached a third predeterminedrotary position short of a second predetermined rotary position whichcooperates with the first predetermined rotary position to define apredetermined rotary angle region where the desired torque is generatedby an electric current flowing in the winding associated with said step(a), for preventing an electric current from flowing in the winding in aregion other than the predetermined rotary angle region.
 2. A drivecontrol method for a variable reluctance type motor according to claim1, further comprising the substeps of:i) determining that the rotorsalient pole has reached the first predetermined rotary position duringthe acceleration mode when the rotor salient pole begins to be oppositethe stator salient pole; and ii) determining that the rotor salient polehas reached the first predetermined rotary position during thedeceleration mode when the rotor salient pole is brought to becompletely opposite the stator salient pole.
 3. A drive control methodfor a variable reluctance type motor according to claim 2, furthercomprising the substeps of:i) setting the second predetermined rotaryposition during the acceleration mode such that the rotor salient polewill be completely opposite the stator salient pole at that rotaryposition; and ii) setting the second predetermined rotary positionduring the deceleration mode such that the rotor salient pole will startto be deviated at that rotary position from a state where it is oppositethe stator salient pole.
 4. A drive control method for a variablereluctance type motor according to claim 1, further comprising thesubstep of setting the third predetermined rotary position in dependenceon an inductance of the winding.
 5. A drive control method for avariable reluctance type motor according to claim 1, further comprisingthe substeps of:i) using a motor rotation speed as the motor drivingparameter; and ii) selecting either one of the acceleration mode and thedeceleration mode in accordance with a difference between a commandvalue of the motor rotation speed and an actual value thereof.
 6. Adrive control method for a variable reluctance type motor according toclaim 1, further comprising the substep of starting the excitation ofthe winding of a next stator salient pole before the third predeterminedrotary position is reached.